 | Term | Definition |
| |
Source-image receptor distance (SID) |
The distance between the tube target and the IR imaging plane |
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High kVp |
Produces a low contrast image |
| |
Low kVp |
Produces a high contrast image |
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Inverse square law |
The relationship between SID and beam intensity |
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Density |
Refers to the overall blackness or darkness of the radiograph |
| |
Radiographic quality factors |
Density, contrast, distortion and recorded detail |
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Prime factors of radiographic exposure |
Milliamperage (mA), exposure time (S), kilovoltage (kVp) and distance (SID) |
| |
Milliampere-Seconds (mAs) |
The primary controller of radiographic density |
| |
Overexposed |
A film that is too dark |
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Underexposed |
A film that is too light |
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Tissue density |
Refers to the mass density of the body part |
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Contrast |
The difference in radiographic density between adjacent portions of the image |
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Penetrometer (step-wedge) |
A solid piece of aluminum with steps of varying thickness |
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High contrast |
Also known as short-scale contrast because the range of densities is short |
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Long-scale contrast |
The low level of contrast produced by high kVp |
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Subject contrast |
The range of differences in the intensity of the X-ray beam after it exits the patient |
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Fog |
A general, unwanted exposure to the film |
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Radiographic contrast |
The product of two separate contrast factors: the film contrast and the patient contrast |
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Distortion |
Refers to differences between the actual subject and its radiographic image |
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Size distortion |
Always in the form of magnification enlargement |
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Shape distortion |
The result of unequal maginification of the actual shape of the structure |
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Magnification |
A result of the geometry of the imaging setup; it is a function of the relationship between the SID and OID |
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Object-image receptor distance (OID) |
The distance between the subject and the IR |
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Foreshortening |
Projects the part so it appears shorter than it really is |
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Elongation |
Projects the object so it appears longer than it really is |
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Recorded detail |
Sometimes referred to as resolution, it is the sharpness of the image |
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Factors which affect recorded detail |
Geometric factors, motion, quantum mottle, focal spot size intensifying screen speed and film and/or screen contact |
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Umbra |
The actual anatomical area, body part or structure shown in the image |
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Penumbra |
The "unsharp edges" of the umbra, or body part |
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Motion |
Any movement during radiography causing blurring of the image, reducing definition |
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Quantum mottle |
When a grainy or mottled (spots) image is created |
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Contrast is primarily controlled by altering the: |
Kilovoltage (kVp) |
| |
An increase in OID will result in: |
Increased magnification |
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Density is primarily controlled by varying the: |
mAs |
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A change from the small focal spot to the large focal spot results in: |
Decreased image sharpness |
| |
If image is overexposed, what change in exposure factor should be used to correct: |
Decrease the mAs |
